The interactions among the nervous system, the endocrine system, and the immune response are now recognized as important for health. Data from a number of studies suggest that various stressors may affect the development of infectious and malignant disease through their impact on the immune response. However, very few studies have used human subjects, and almost nothing is known about the immunological sequelae of repeated stressful events in humans. Since repeated stressful events have important effects on immune function and health, fluctuations in immune function will be measured in healthy adults following repeated exposure to the same stressor, examinations. The psychological literature suggests that faulty or prolonged efforts at adaptation lower physical resistance, increasing the probability of illness. However, since only a minority of individuals become ill following stressful events, individual differences are thought to mediate the stress-associated illness. This proposal also addresses the extent to which hardiness, a stress-resistant personality style, moderates adverse psychological and immunological changes. Hardiness has three components: a sense of personal control over stressful events, feelings of involvement or commitment in daily activites, and a belief that life changes offer interesting challenges, rather than threats. Serial samples will be collected from 90 male first-year medical students (30/year) over a three-year period. Immunological and self-report data will be collected during the first, third, and fifth (final) examinations, as well as one month before each. Comparable data will also be collected concurrently from a control group of 45 age- and sex-matched donors (15/year) who are not experiencing cyclical stressors. Certain aspects of cellular immunity will be assessed. In addition, since poor nutrition can adversely affect cellular immunity, nutritional assays will be included in the battery of tests. Data on health status will be collected each time blood is drawn and related to the hardiness variable and the immune functions tested.